1. Field of the Invention
This invention relates in general to refrigeration systems and, in particular, to the screw compressor employed in such systems. More specifically, but without restriction to the particular embodiments hereinafter described in accordance with the best mode of practice, this invention relates to an oil management system for the inlet pipe of a screw compressor employed in a chiller type refrigeration system.
2. Discussion of the Related Art
Screw compressors are commonly employed in a number of applications from providing pressurized air for pneumatic tools to circulating a refrigerant through the refrigeration cycle in a cooling system. One particular use of the screw compressor is in a refrigeration system commonly known as a chiller. In addition to the screw compressor, the typical chiller also includes a condenser, an evaporator or cooler, an oil-refrigerant separator, a refrigerant storage tank, and a throttling valve. These components are connected to each other by tubing that carries the refrigerant through the system. The evaporator typically includes a plurality of tubes that circulate water in a closed loop to another heat exchanger or cooling coil. At the cooling coil, circulating room air is induced through the cooling coil by a fan so that heat is removed from the circulating room air.
The components of the chiller are customarily arranged relative to one another such that the suction inlet pipe of the screw compressor is directed downwardly into the evaporator. The screw compressor is lubricated in part by oil draining from the compressor bearings being entrained into the suction gas entering the rotors. The combined oil and refrigerant mixture is carried through the compression cycle and then discharged into the system separator where the oil is removed from the refrigerant. During low load operation of the chiller, there is insufficient gas velocity to effectively entrain this oil into the gas flow entering the compressor. At this level of operation, it is common for lubricating oil to continuously flow down the suction inlet and into the evaporator where it has the undesirable effect of mixing with the refrigerant. In this manner, oil is lost from the compressor resulting in an insufficiently lubricated compressor and a reduction in chiller performance caused by the presence of large quantities of oil in the refrigerant circuit.
There has been proposed various solutions attempting to solve the problem of this type of oil loss in a screw compressor operating at reduced loads. These solutions include simply preventing the compressor from operating at loads low enough to cause this type of oil loss, installing baffle arrangements designed to catch the oil and return it to the compressor by use of an ejector system, and employing a distillation process to remove the excess oil from the refrigeration circuit. The first solution is inappropriate in many applications requiring low load operation of the screw compressor. The last two proposed typify solutions that involve extensive design modifications which add a significant cost to manufacturing the refrigeration system.